This invention relates to room temperature curable organopolysiloxane compositions, and more particularly, to room temperature curable organopolysiloxane compositions which cure into elastomers having improved oil resistance, coolant resistance and water resistance.
Various types of room temperature curable organopolysiloxane compositions are well known in the art which cure into elastomers at room temperature upon contact with air-borne moisture. Among others, those compositions of the type that cure while releasing alcohol are preferentially used in sealing, bonding and coating of electric and electronic equipment, owing to their advantageous features of no disgusting odor and no corrosion of metals. One typical composition of this type is described in JP-B 39-27643 as comprising an organopolysiloxane end-blocked with hydroxyl groups, an alkoxysilane, and an organic titanium compound. Also JP-A 55-43119 discloses a composition comprising an organopolysiloxane end-blocked with alkoxysilyl groups, an alkoxysilane, and alkoxy titanium. JP-B 7-39547 discloses a composition comprising a linear organopolysiloxane end-blocked with alkoxysilyl groups (including silethylene), an alkoxysilane, and alkoxy titanium.
However, these compositions lack oil resistance and long-life coolant (LLC) resistance which are requisite when used in proximity to automotive engines.
An object of the invention is to provide a room temperature curable organopolysiloxane composition which cures into an elastomer whose physical properties change little even when used under rigorous conditions as encountered in proximity to automotive engines, and which remains stable during storage under sealed conditions.
It has been found that by using as the base polymer a branched organopolysiloxane having at least one radical of the general formula (1) or (2), defined below, at an end and at least one radical of the general formula (1) or (2) on-a side chain of the polymer, or a branched organopolysiloxane having at least two radicals of the general formula (1) or (2) only on side chains of the polymer, and combining it with silica, an organooxysilane or partial hydrolytic condensate thereof, and a condensation catalyst, there is obtained a room temperature curable organopolysiloxane composition which is improved in stability during storage under sealed conditions and cures into an elastomeric product whose physical properties change little even when used under rigorous conditions as encountered in proximity to automotive engines, as compared with prior art room temperature curable organopolysiloxane compositions of the one part, alcohol-removal type.
The invention provides a room temperature curable organopolysiloxane composition comprising, as essential components,
(A) 100 parts by weight of a branched organopolysiloxane having at least one radical of the general formula (1) or (2) at an end and at least one radical of the general formula (1) or (2) on a side chain of the polymer, or having at least two radicals of the general formula (1) or (2) only on side chains of the polymer,
(R1O)aR23-aSixe2x80x94Oxe2x80x94xe2x80x83xe2x80x83(1)
(R1O)aR23-aSixe2x80x94Yxe2x80x94SiR22Oxe2x80x94xe2x80x83xe2x80x83(2)
wherein R1 is a monovalent hydrocarbon group or alkoxy-substituted monovalent hydrocarbon group, R2 is a monovalent hydrocarbon group, xe2x80x9caxe2x80x9d is 1 to 3, and Y is a divalent hydrocarbon group having 1 to 8 carbon atoms,
(B) 1 to 40 parts by weight of fumed silica,
(C) 0.5 to 25 parts by weight of an organooxysilane having the general formula: R3bSi(OR4)4-b wherein R3 is a monovalent hydrocarbon group, R4 is a monovalent hydrocarbon group or alkoxy-substituted monovalent hydrocarbon group, and xe2x80x9cbxe2x80x9d is 0 or 1, or a partial hydrolytic condensate thereof, and
(D) 0.1 to 10 parts by weight of a condensation catalyst.